Reclassification based on cladistics
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Question
What is a clade?
Answer
A group made of **one common ancestor and ALL of its descendants** — nothing left out, nothing unrelated added in.
Question
What does 'monophyletic' mean?
Answer
It describes a **valid clade** — an **ancestor plus all its descendants**. Cladistics aims to make every named group monophyletic.
Question
When are organisms reclassified by cladistics?
Answer
When **molecular/cladistic (DNA) evidence conflicts** with the traditional **morphology-based** grouping, showing the old group is **not a clade**.
Question
Why was the figwort family (Scrophulariaceae) split?
Answer
**DNA** showed its members did **not share a single common ancestor** (it was not a clade), so it was **split and reorganised** into several smaller true clades.
Question
Why are birds placed inside the reptile clade?
Answer
Cladistics places birds **inside the dinosaur/reptile lineage** (closest to crocodiles); a 'reptile' group without birds is **paraphyletic**, so to be a clade it must **include birds**.
Question
Why might a species be moved between genera?
Answer
If **DNA** shows its true closest relatives are in a **different genus**, it is **moved (and renamed)** so the genus stays a **monophyletic clade**.
Question
What does reclassification tell us about classification?
Answer
That it is **provisional and evidence-led** — the **current best hypothesis** of relationships, open to revision when better molecular data arrives.
Question
Why can grouping by appearance (morphology) mislead?
Answer
Unrelated species can **look alike** (convergent evolution) and close relatives can **look very different**, so a looks-based group may mix lineages or split real ones.
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Topic 1.7 hub
Classification and cladistics
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